1. Field of the Invention
The present invention relates to exposure devices such as those used to manufacture liquid crystal display panels.
2. Description of the Related Art
For many years, liquid crystal display (LCD) panels have been used in word processors, personal computers, televisions, and other display-oriented devices. To manufacture such liquid crystal display panels, it is necessary to produce patterns on transparent conductive films, amorphous silicon films, or the like disposed on glass or similar substrates by means of photolithography.
To facilitate such photolithography, step and repeat type exposure devices often are used. Such devices typically perform exposure projection of an original picture pattern formed on a mask onto a resist film disposed on a glass substrate via a projection optical system. Such exposure devices have become quite reliable in terms of facilitating manufacture of LCD panels. Unfortunately, however, as LCD "picture" sizes have increased, so too have the sizes of glass plates, masks, and exposure regions. Such increased sizes have led to several problems which have not heretofore been effectively addressed and solved.
For example, to design an enlarged projection optical system to produce relatively large LCD panels, it has become necessary to produce large optical elements that can support very high accuracy and the like. Such accuracy comes at a high price. For example, manufacturing costs are increased whenever greater device accuracy is required. Furthermore, larger optical systems require larger device infrastructures which causes increases in costs associated with device manufacture, transportation, and installation. And, to exacerbate such problems, increased exposure device size often results in poorer image projections and the like.
To address such problems, various exposure devices have been proposed. For example, as shown in U.S. Pat. No. 5,625,436, the inventors thereof proposed using a projection optical system unit consisting of plural projection optical system modules. More particularly, the inventors proposed using a scanning type exposure device of a multi-lens projection optical system which performs equal and multiple exposures while simultaneously causing a mask and substrate to move. Scanning is done while fixing in place an illuminating optical system and a projection optical system unit. By simultaneously moving the mask and a substrate, an exposure pattern (e.g., a rectangular pattern) formed on a surface of the substrate moves and, as a result, a whole exposure is achieved. When using such a projection optical system which is not very large in comparison with the size of the mask and substrate, exposure becomes possible in a region of a comparatively large image plane.
The device shown and described in the '436 patent incorporates a single projection optical system. As such, after plural projection optical system modules were assembled into the exposure device, the same were inspected by inspection devices for accuracy. Then, after an accuracy inspection, the single-part projection optical system was loaded into the exposure device. In such an inspection device, as a mask used for inspection, in at least one scan direction and a direction about at right angles, using a large mask to about the same degree as a mask used in practice, the projection optical system unit was inspected and adjusted. As such, the adjustment of the projection optical system unit was time-consuming and, in addition, the inspection device became large.
Together with larger substrates, it was necessary to make masks larger. As masks became larger, the same were recognized to bend under their own weight and size. As a result, the bending amount was large at a center portion of a mask, and became small at side portions thereof. For example, in order to perform exposure of a large substrate of say about 500 mm.times.650 mm, it was not uncommon to realize up to 40 .mu.m in bending. As such, even when correctly positioned in accordance with an exposure pattern formed on a surface of a substrate there was concern that bending would cause distorted projections, etc.
Thus, there exists a need to provide new and improved scanning type exposure devices which may be used to manufacture LCD panels and the like having relatively large dimensions and surface areas. To be viable, such devices must effectively address the problems stated above and, in particular, those related to mask bending.